Application of the Streeter-Phelps model for evaluating the wastewater treatment plant effluent impact on the receiving river water quality

Al-Zubaidi, HAM, Al Yousif, MA, Kadham Obaid, M, Naje, AS, Al-Saeedy, FAZK, Al-Khafaji, FMA, Chelliapan, S and Hashim, K ORCID: 0000-0001-9623-4060 (2026) Application of the Streeter-Phelps model for evaluating the wastewater treatment plant effluent impact on the receiving river water quality. Journal of Ecological Engineering, 27 (6). pp. 136-147. ISSN 2081-139X

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Abstract

Water is considered one of the most important natural resources on Earth. Rivers are the main source of freshwater in many countries around the world. However, these rivers are exposed to pollution due to several factors, the most significant of which is the direct discharge of partially treated or untreated municipal wastewater into receiving rivers. This leads to an increase in the river carbonaceous biochemical oxygen demand (CBOD), which in turn causes a decrease in the dissolved oxygen (DO) levels. In this study, the Streeter-Phelps model was used to evaluate the impact of the Al-Muamirah Wastewater Treatment Plant on the water quality of the Hilla River in central region of Iraq and to monitor the variation in the CBOD and DO values over distance from the wastewater discharge point. The results indicated that very good accuracy was achieved by the developed model compared to field data. The highest CBOD value was at the wastewater effluent location, leading to a direct decrease in the DO levels. Subsequently, the river experienced a self-purification process that restored oxygen levels to its background value. However, the high CBOD values caused that oxygen concentrations at some distances have fallen below the permissible limit, with the lowest dissolved oxygen concentration of 4.7 mg/L recorded at 20 km from the wastewater discharge point. The results also showed that the highest acceptable 5-day CBOD value of wastewater effluent that can be discharged into the river water without lowering the dissolved oxygen level below the minimum permissible value, was 8.4 mg/L, making the minimum level location (at about 15 Km) closer to the effluent outfall. Furthermore, the river oxygen sag curve was very sensitive to the CBOD decay and oxygen reaeration coefficients variation Accordingly, the study recommended continuous monitoring of CBOD levels in the treated wastewater effluent and implementing additional treatments, when necessary, to ensure the preservation of water quality and to prevent any adverse impacts on its environmental conditions.

Item Type:	Article
Uncontrolled Keywords:	4004 Chemical Engineering; 40 Engineering; 4011 Environmental Engineering; 6 Clean Water and Sanitation; 3103 Ecology; 4011 Environmental engineering
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TD Environmental technology. Sanitary engineering
Divisions:	Engineering and Built Environment
Publisher:	Polskie Towarzystwo Inżynierii Ekologicznej (PTIE) – Polish Society of Ecological Engineering
Date of acceptance:	16 April 2026
Date of first compliant Open Access:	2 September 2026
Date Deposited:	02 Sep 2026 14:54
Last Modified:	02 Sep 2026 14:54
DOI or ID number:	10.12911/22998993/216357
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29306

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